This invention relates to centrifugal oil/water separators designed for removing relatively small amounts of oil from large water streams. More specifically, this application pertains to a device for removing vapor entrained in the inlet water flow to avoid cavitation within such a separator device.
My prior U.S. Pat. Nos. 3,791,575 and 3,890,347 best describe the state of the art in devices designed for separating relatively small amounts of oil from relatively larger amounts of water. Such fluid streams may be found, for example, in the ballast tanks of oceangoing vessels or in other systems wherein large volumes of waste water must be disposed of without the danger to the environment which would occur if small amounts of oil were allowed to be disposed of along with the water. The first of my prior patents, U.S. Pat. No. 3,791,575, is directed to the basic concept of controlling the oil/water interface within a centrifugal separator by comparing the pressure at the emulsion input to the pressure at the oil outlet. The second Pat. No. 3,810,347 is directed toward an arrangement for removing entrained vapors from a foamy input emulsion, the vapor removed as a separate by-product from the separator. While the latter patent provides for the centrifugal separation of vapors from the liquid input element, it does not adequately provide for the removal of bubbles which enter the centrifugal separator to form a vapor pocket at the input impeller of the separator. Such vapor pockets generally do not occur as a consequence of the foamy emulsion described in U.S. Pat. No. 3,810,347 but rather occur as a consequence of vapor bubbles in an otherwise liquid stream. The bubbles are therefore transferred separately in the inlet stream to the separator and are easily separated from the remaining stream flow prior to the centrifugal action of the separator. For this reason, such bubbles can accumulate at the separator input in the input impeller chamber and, if allowed to accumulate to a sufficient extent, can create cavitation in the input impeller. Since this input impeller is necessary for maintaining pressure balance within the separator system, that is, for reducing pressure loss through the system, it is imperative that such cavitation be prohibited. In prior art systems wherein no mechanism was included for the removal of such vapor accumulations, it has been found necessary to periodically stop the separator to purge the inlet channel and to then reactivate the system for a period of time until subsequent vapor accumulations exist.